The USB Communications Device Class (CDC) allows to convert the USB device into a serial communication device. It is an abstract USB class protocol defined by the USB Implementers Forum.
A target device running emUSB-Device CDC is recognized by the host as a serial interface (USB2COM, virtual COM port), without the need to install a special host driver, because the communication device class is one of the standard device classes and every mayor operating system already provides host drivers for those device classes. All PC software using a COM port will work without modifications with this virtual COM port. Under Windows the device will show up as a COM port, under Linux as a /dev/ACMx device. This allows the user to use host software which was not designed to be used with USB, such as a terminal program.
The start application (in the Application subfolder) is a simple echo server, which can be used to test emUSB-Device. The application receives data byte by byte and sends it back to the host.